TOPIC: subnet mask

hi everyone
i was jus wonderin why isit that with a subnet mask of
255.255.255.0 we can have one subnet and 254 hosts?
i noe why 254 hosts...coz 2^8-2=254
but why one subnet?
thanx a million in advance:)

I'm not sure what you are asking here. But 255.255.255.0 is not subnetted, unless your address happens to start with anything less that 192, then you have a subnetted address.

If not, you have a class C address and no subnet. If you subnet this address, you will not have 254 hosts any more. Each subnect "split" will lose you addresses, as each subnet will need to drop 2 addresses for network and broadcast.

its actually from the celticrover site....one of the ACCESS LIST LABS-telnet

the router has a serial and an ethernet interface, and we are supposed to block telnet access into the router...
the serial interface is connected to the rest of the network...
the ethernet int is connected to the host

the ans given -the router was configured such that theres an access list placed at both the interfaces denying access to the router.

I don;t understand why there should be an access-grp at interface serial with an "in"